Magnetic recorder utilizing an energizing oscillating circuit



Feb. 25, 1947. M, CAMRAS E1- AL 2,416,610

MAGNETIC RECORDER UTILIZING AN ENERGIZING OSCILLATING CIRCUIT Filed Dec.26. 1942 4 Sheets-Sheet 1 Mmew (301246, 2/! rue/v0 f. ZEIWVEE.

1947- M. CAMRAS ETAL MAGNETIC RECORDER UTILIZING AN ENERGIZINGOSCILLATING CIRCUIT Filed Dec. 26, 1942 4 Sheets-Sheet 2 EA VHOIVD EZEN/v59.

Feb. 25, 1947. CAMRAS, ETAL 2,416,610

MAGNETIC RECORDER UTILIZING AN ENERGIZING OSCILLATING CIRCUIT Filed Dec.26, 1942 4 Sheets-Sheet 3 lVAfW/V 04/16/96. Ean-m/vo 5 ZEN/V58.

Feb. 25, 1947. NLCAMRAS ETAL MAGNETIC RECORDER UIILIIZINCT AN ENERGIZINGOSCILLATING CIRCUIT Filed Dec. 26, 1942 4 Sheets-Sheet 4 N V I FEF'Z IMaewzv Cnmenq. 4,410 5 Zewmne.

bluipn 7 time while still operating the vehicle.

Patented Feb. 25, 1947 MAGNETIC RECORDER UTILIZING AN ENERGIZINGOSCILLATING CIRCUIT Marvin Camras, Chicago,

Zenner, Brookfield, 111., asslgnors to Armour Research Foundation,Chicago, 11]., a corporation of Illinois ApplicatlonDecember 26, 1942,Serial No. 470,209

3 Claims. (Cl. 179100.2)

This invention relates to improvements in a magnetic recorder of thetype which makes 9.

sirable for use on airplanes, patrol boats, and

other vehicles which may for some reason become out of contact withheadquarters, although the invention will have other uses and purposesas will be apparent to one skilled in the art.

Magnetic recordersfor airplanes, as well as other vehicles normally'crowded with instruments, should be extremely compact and extremelylight in weight. In many cases it is also desirable to have themportable rather than built in or seated within a built-in receptacle.The uses of the magnetizing devices are many indeed, both for militaryand civilian work, such as observation or recognizance recordings,establishment of flight logs, recording of all conversations betweenparties in the vehicle, instructor and student conversations, etc.,thereby giving records of the particular trip far more complete than areavailable by other methods. Consequently, it is desirable to have thesedevices functioning at all times, and repairs, when necessary, should beextremely simple to make, or even possible for the occupant of thevehicle to make in a very short Likewise, the outside connections shouldbe simple. Further, in the conservation of space, lightness of load,etc., it is desirable to take all possible advantages of the equipmentincorporated in the recording device.

With the foregoing in mind, it is an important object of the instantinvention to provide a magnetic recording device of extremely compactconstruction which is highly economical to both manufacture and operate.

Another object of the invention is the provision of a magnetic recordingdevice of compact construction. which with the exception of the drivingmember for movable parts, carries all the necessary amplifying circuitand other energizing means necessary in the making of a recording.

Still another object of the invention is the provision of a magneticrecording device in which substantially all of the wiring and associatedapparatus necessary for the making of a recording are carried in aunitary container which may be readily removed and replaced, so that ifanything in connection with the recording circuit becomes out of order,it is a simple expedient to lzsssulz JUL 3 1951 and Raymond E.

2 remove the entire container, replace it with a new one, and proceed tooperate the device. The removed container may then be examined atleisure and repairs made to its contents without incapacitating thedevice or delaying the use of the device. A spare container. may becarried by the pilot of an airplane, or the operator of some othervehicle, and if anything goes wrong with the recording circuitconnections, it is a very simple operation for him to remove a containerfrom the machine and slip in the substitute container.

Also a feature of the instant invention is the provision of a magneticrecording device wherein advantage may be taken of certain of theapparatus embodied in the device to perform additional functionsnormally considered outside the scope of the device.

A further feature of the invention resides in the provision of amagnetic recording device including an amplifying circuit, which circuitmay function as the amplifier for an intercommunication system betweenthe pilot of the vehicle and any others aboard the vehicle, so. that aseparate intercommunication system is not necessary when the magneticrecording device is used on a particular vehicle. Still another objectof the invention resides in the provision of a magnetic recording devicewhich may be associated with the intercommunieating system on a vehiclein such a manner that the device will listen in and also make a recordof the entire conversations between parties in the vehicle.

Another object of the invention is the provision of a magnetic recordingdevice in which the moving parts may be, driven from the batterynormally associated with a vehicle in which the device is being carried,the device being equipped with its own speed control means.

Still another object of the invention is the provision of a magneticrecording device. of simplified and compact construction, wherein theentire mechanism is carried by two frame panels held in confrontingspaced relation with each other.

An additional feature of the invention resides in the provision of amagnetic recording device equipped with a unified form of level windingdevice to control the proper unwinding of the recording medium from onespool and the proper winding of that medium on another spool.

A still further feature of the invention resides in the provision of acompact magnetic recording device in which the recording medium is woundoff one spool and onto another spool, with the device equipped withmeans to prevent coasting or over-run at either spool so as to maintainat all times the proper tension on the recording medlum.

Still another object of the invention resides in the provision of acompact and simplified magnetic recording device wherein only oneexternal connection is necessary, that is, all connections with thedevice being made at one point.

While some of the more salient features, characteristics and advantagesof the instant invention have been above pointed out, other will becomeapparent from the following disclosures, taken in conjunction with theaccompanying drawings, in which:

Figure 1 is a side elevational view of a magnetic recording deviceembodying principles of the instant invention;

Figure 2 is a top plan view of the structure of Figure 1, with certainparts removed for purposes of clarity;

Figure 3 is a fragmentary vertical sectional view, with parts omitted,taken substantially as indicated by the staggered section line III-HI ofFigure 2, looking in the direction of the arrows;

Figure 4 is a fragmentary transverse vertical sectional view through thelevel winding arrangement, taken substantially as indicated by the lineIV-IV of Figure 3;

Figure 5 is a fragmentary plan sectional view of the governingarrangement, taken substantially as indicated by the line VV of Figure3;

Figure 6 illustrates a simplified schematic diagram of the amplifying,recording, and intercom.- municating circuit; and

Figure '7 is a simplified schematic diagram illustrating the circuitconnections for the' driving member.

As shown on the drawings:

The illustrated embodiment of this invention as shown includes only thenecessary structural or frame parts, and any exterior decorative,fireproof, or other type of cover or container has been omitted forpurposes of clarity, since the device as illustrated may be incorporatedin any suitable form of transporting container, built-in receivingdevice, etc., as may be most desired.

In the-illustrated embodiment of this invention there is shown a pair ofspaced confronting panel members I and 2 which support all of thestructure embodied in the invention, and which may be of any suitablematerial such as metal, plastic, etc. These panel members I and 2 areheld in fixed spaced relationship relatively to one another by aplurality of bolt and sleeve connections 3, one in each corner region ofthe panels. It will be understood that all cross shafts are suitablysupported where necessary, adequate bearings for the journals being usedwhere necessary, and if the shaft is normally stationary, a propermounting will be associated with each panel, it not being'necessaryherein to describe such details of construction.

On the outside of the panel I a reel 4 is mounted on the projecting endof a shaft 5, which is rotatable but undriven. This reel or spool 4carries a recording medium which, in the illustrated instance, is in theform of a fine round wire 6 and is the supply spool from which the wire6 is wound onto another similar reel or spool 'I carried on theprojecting end of a. driven shaft 8. As the Wire 6 travels from thespool 4 to the spool 1, it first passes under a positioning pulley 9,then a guide pulley I0, then through or over a, mag-' netic recordinghead disposed in a casing II, thence over another guide pulley I2 and tothe spool I. The positioning pulley, both guide pulleys, and therecorder head in its casing II, are all mounted upon a reciprocablecarrier I3 associated with level winding equipment, this entire carriermoving backward and forward to insure a level winding of the wire 6 uponthe spool I.

With reference more particularly to Figure 2, it will be seen that thepositioning pulley 9 is of such shape as to tend to position the wire 9so that. any final straightening may be done by the guide pulley I9.Even though the wire 6 may be out of alignment on the reel 4, the pulley9 is so shaped that it together with pulley I II will center this wirewith respect to the recording head. The guide pulleys I0 and I2 are sopositioned as to hold the wire properly in contact with the recordinghead. All of the pulleys 9, I0 and I2 are merely mounted on subshaftsfor free rotation by the friction of the wire passing over thesepulleys.

As the wire 6 travels through the recording head in the casing II thewire is magnetized in accordance with whatever sound is received by apick-up microphone and by means of an electrical circuit to be laterdescribed. Thus, a recording is made on the wire which recording may belater reproduced from the wire at some other location with suitablereproduction equipment. In the event the device is used in an airplane,or some other vehicle, conversations between occupants of the vehiclemay be recorded on .the wire for later reproduction.

During operation, the wheel I is driven and pulls the wire 6 from thereel 4 over the pulleys 9, I0 and I2 and through the recorder headcasing II. All of the pulleys as Well as the reel 4 turn in response tothe pull of the wire. The drive means for actuating the reel 1 includean electric motor I4, seen best in Figure 3, which motor is carriedbetween a pair of suitable transverse supports I5 and I6, spot welded orotherwise secured to the supporting panels I and 2. This motor may beenergized by current from any suitable source, such as the batterycarried by the vehicle in which the device is being used. In order tomaintain a constant speed of the motor, and therefore a constantmovement of the recording medium or wire 6, the motor is preferablyself-governed, and to that end a centrifugal governing arrangementgenerally indicated by numeral I1 is carried by the motor shaft I8. Thisgoverning arrangement is best seen in Figures 3 and 5, and includes adisk I9 on the motor shaft, on which disk is a laterally extendingcontact arm 20 attached at one end to an upstanding bracket 2I. Oppositethe contact arm 20 is another similar contact arm 22 attached at one endto a similar bracket 23. While the motor is running at a predeterminedspeed, these contact arms remain in position with, their respectivecontact points closing a circuit. A stop member 24 carried in a bracket25 determines the position of the contact arm 20. The contact arm 22 isfree to move away from the contact arm 29 and centrifugal force due tothe speed of rotation is sufficient to overcome the inherent tendency ofthe spring contact arm 22 to remain in original position. An upstandingstop member in the form of a post 26 limits the circuit breakingmovement of the contact arm 22.

As will more fully later appear, the contact arms 20 and 22 control thecircuit through the nate wastage of the wire.

- made.

spring contact 22 to overcome the centrifugal force and again close thecircuit. Thus, during operation, the motor and likewise all parts drivenby the motor, including the spool or reel 1, will be actuated atsubstantially constant speed.

The drive connection between the reel 1 and the motor includes avertically disposed worm gear 21 on the upper'end' of the motor shaft,enmeshed with a worm wheel 28 keyed to the aforesaid shaft 8.

During operation of the recording device, it is preferable to maintain apredetermined tension on the wire 6 above the tension necessary torotate the reel 4, in order to eliminate possible breakage of the wireand also in order to elimi- Further, it is desirable to prevent over-runof the wire due to coasting of the reel 4 in the event a sudden stop isTo this end, a floating ratchet wheel 29 is freely carried by the shafton the outer end of which the reel 4 is affixed. On one side of thisratchet wheel is a collar 3|] fixed to the shaft and carrying a frictionclutch plate 3|. On the opposite side of the ratchet wheel is a frictionclutch plate 32 keyed to the shaft 5, but slidable thereon, and thisclutch plate is urged into side surface contact with the ratchet wheelby means of a suitable spring 33 bearing against the plate at one endand against a fixed collar 34 at the other. A detent 35 carried on asupporting member 36 is in engagement with the ratchet wheel to preventrotation of this wheel in a forward direction or in the direction ofmovement of the reel 4 when the wire 6 is being wound onto the reel 1.When the reel 4 rotates forwardly, the ratchet wheel is held stationaryby the detent. Consequently,friction clutch engagement with both sidesof this ratchet wheel provides a frictional tension tending to resistrotation of the reel 4, and therefore a predetermined tension is on therecording medium or Wire 6 at all times during movement of the wire. Inthe eventa sudden stop occurs, the friction clutch engagement with theratchet wheel prevents any over-run-of the reel 4, and thus theunintentional production of a slack loop in the wire 6.

When reels are changed, or after reconnection of the wire 6 following abreakage, or for some other reason when some adjustment is made in thewire, the engagement of the detent 35 with the ratchet wheel 29 permitsa free backward rotation of the shaft 5 so that the wire may beinitially stretched taut prior to beginning operation.

The level winding arrangement is also driven through a gear train fromthe motor |4. Obvi ously, the level winding arrangement must operate ata much slower rate of speed than the reel 1 rotates. Therefore there isa reduction gear train involved including a gear 31 on the rear end ofthe shaft 8 carrying the receiving reel or spool I, which gear isenmeshed with the larger gear 38 carried on a stub-shaft together with asmaller gear 39 which meshes with a larger gear 40 on a shaft 4|. Thisshaft 4|, as best seen in Figure 4, is provided with reverse screw levelwinding slots 42. A yoke or link 43, provided with a hub 44 floatingover the reverse screw slot 42, carries a level wind. rider 45 whichmoves the yoke back and forth along the shaft 4| as this shaft 4|rotates continuously in one direction.

At one end thereof, the yoke 43 has a hub 46,

looked as indicated at 41 to a slidable supporting rod 48 attached tothe aforesaid carrier l3 5 and freely slidable in suitable bearingmembers in the supporting panels I and 2. At the lower end'thereof theyoke is provided with a similar hub 49 locked to a similar slidablesupporting rod 50 which is also fixedly attached to the same carrier.I3. It is therefore apparent that as the shaft 8 carrying the receivingspool I is rotated by the motor M, the shaft 4| will be rotated in thesame direction through the above described gear chain, and as this shaft4| rotates the supporting rods 48 and 50 will be moved in and outaxially a distance corresponding to the length of the reverse screw slot42, thus moving the pulleys 9, l0 and I2 together with the recordinghead in the casin backward and forward across the circumferentialsurfaces of the reels 4 and 1 and effectively cause a level winding ofthe recording medium on the receiving reel 1.

With the exception of the energy for operating the motor I4, all of thepower necessary for the amplifying and oscillating circuits, as well asthese circuits, are contained within the structure disposed between thesupporting panels I and 2. The main amplifying and oscillating circuitincluding the necessary vacuum tubes, as

well as the necessary transformers, are all packed within or mounted ona container-5| which is illustrated in the form of'a rectangularopensided box, and this container is slidable in the manner of a drawerbetween the panels I and 2 and in tracks defined by a pair of spacedangle bars 52 and 53 on each of the panels I and 2. The drawer orcontainer 5| seats on a similar pair of angle bars 54, one on each ofthe panels I and 2, as best seen in Figures 2 and 3. In one of the sidewalls of the container 5| sockets are provided for accommodating twovacuum tubes 55 and 56, these being all of the vacuum tubes nec-, essarywith the particular circuit utilized in the illustrated form of theinvention. The tube 55,

as will more fully later appear herein, is a composite tube embodied inthe amplifying circuit, and is illustrated in the diagram of Figure 6for purposes of convenience as two separate tubes 55a and 5517, althoughin actual practice it is preferable to utilize a composite tubeembodying all of the structure and characteristics of both tubes a and55b in a single tube 55. The tube 56 is incorporated in the oscillatingcircuit.

The drawer or container 5| also carries the 55 necessary transformerssuch as the transformer 51 visible in Figure 3, and also carries one ofthe power sources in the form of a battery 58. The structure isillustrated in Figure 3 in a some what diagrammatic form, theconnections being broken away, but it is to be understood that thevarious connections of the transformers and other associated apparatuswill be contained within the drawer 5| as much as possible, and theseconnections are best shown in the diagram of Figure 6.

Another supporting arrangement in the form of a pair of spaced anglerails or tracks 59 and 60 is mounted on the panel 2 which, together witha bottom rail 6| also on the panel 2 (Figure 3) and another verticalrail 52 on the inside of the panel I (Figure 2) provide a receivingsocket for a B-battery 63. In view of the fact that if anything becomeswrong with the B-battery it is only necessary to substitute a newbattery for the 76 oldone, it is not necessary to include the B 7battery 88 within the above discussed drawer or container The B-batteryis merely'connected by a pair of conductors 84 and 85 to a plugconnector 88 engageable in a suitable socket in the wall of thecontainer 5|, as seen clearly in Figure 8.

It is desirable, for the sake of'simplicity and expediency, to have onlyone connection from outside apparatus to the magnetic recording device.To this end, the illustrated embodiment of the invention is soconstructed and arranged that it is only necessary to connect one socketconnector with a plug connector 61 located between the panels land 2with its projecting contact members 88 extending beyond the area definedby the panels, as seen in Figures 2 and 3., From this plug 81 variousleads generally indicated by numeral 68 extend to connections for themotor I, and also to a plug 89 which may be engaged with a complementaryconnector in the bottom of the drawer or container 5|. The single plug81 is sufiicient for connecting the battery of the vehicle to the motorto drive the latter, and also to connect earphones, microphones, andsimilar apparatus with the recording circuit. Thus, the earphones andmicrophones may be located at any convenient place in the vehicle,together with the necessary switches for energizing them, and haveconductors therefrom extending to one single plug. The conductors=fromthe vehicle cattery may also extend to the same plug. It is a simpleexpedient'when the magnetic recording device is placed in position toconnect that plug to the device, and everything includingintercommunication between the occupants of the vehicle and making of arecording is ready for operation.

With reference to Figure 3, it will be seen that a suitable platform 18supports connections to the motor by way of the automatic governingdevice I9, and this platform also carries several condensers 1| and 12and 13, the latter being seen in Figure 5, associated with the motorcircuit as will more fully later appear herein.

The recording head contained in the casing l is best seen in Figure 6and includes a core 14, preferably laminated, and is substantiallyrectangular in shape with the exception of a rather minute air gapdividing the upper leg of the core so as to provide opposed pole facesadjacent the air gap.- The recording medium or wire 8 travels through aslot in the upper leg of the core as indicated by dotted lines in Figure6, A magnetizing coil 18 is wound around one leg of the core and theimpulses through this coil 18 are of varying magnitude in keeping withthe variation of the voice or other sound being recorded. The impulsesfrom the coil 18 are transferred to the wire 5 in the form ofmagnetizations of the wire. As the wire travels through the slot in thepole faces, successive increments of the wire are magnetized in theregion of the air gap 15 in accordance with the sound being recorded.

In Figure 6 a diagram of a suitable circuit arrangement for the properoperation of the magnetic recording device in both its phase as arecorder and as a means of intercommunication is schematicallyillustrated. In this circuit the particular batteries, conductors, tubesand similar apparatus above referred to in connection with the showingsin Figures 2 and 3 are included and, of course, carry the same referencenumerals.

This circuit includes the battery 58, carried in the container 5|,conncted to energize a microphone 11 or equivalent pick-up device, thecur-' rent passing from the battery through a conductor 18, provided themanually controlled switch-18 is closed, to the microphone, and from themicrophone through a conductor 80 to the primary of a step-uptransformer 51, and from the primary through conductors 8| and 82 backto the opposite side of the battery 58. As indicatedby dotted lines inthis figure, a second microphone Ila maybe connected in parallel withthe microphone 11, and likewise as many microphones or other pick-updevices as may be desired may be similarly included in the circuit. Asindicated at 88, the conductor 8i is preferably also grounded.

As pointed out above, the vacuum tubes 55a and 55b, in actual practice,are preferably embodied in a single tube 55, but for purposes of claritythe composite tube is separated into its constituent parts in the wiringdiagram, and 55a is indicated in the circuit as the first stage ofamplification, while tube 55b provides the second amplification stage.By means of these amplification stages, the stepped-up voltage from thesecondary of the microphone transformer 51 is successively amplified.

The secondary 84 of the microphone transformer 51 is connected at oneend to the aforesaid conductor 8|, and thus through conductor Thus, itwill be seen that stepped-up voltages v of varied intensities areinduced in the secondary 84 of the transformer 51 by variations of soundpicked up by the microphone 11, and these stepped-up voltages areapplied across the grid and filament of the tube 55a. The output voltagefrom the tube 55a is appliedacross the grid and filament of the secondamplifying tube 55b through a conductor 81 connected to a grid 88 of thetube 55b. The output from the tube 55b is applied through conductor 89leading from the plate of this tube to a primary coil 90 of a step-downtransformer 9|, the other endof the primary coil being connected throughconductor to the opposite side of the B-battery 83, thus completing thecircuit through the two stages of amplification, the B-battery, and theinput and output transformer coils. A condenser 92 is preferablyconnected across the battery between conductors 84 and 85 to preventalternating current from reaching the B-battery 83. A coupling condenser93 is included in the conductor 81 leading from the plate of tube 55a tothe grid 88 of 55b, to reduce the passage of low frequency volt-v age inthis conductor. The grid 88 of the tube 55b is biased by a resistance 94and a set of biasing cells 85 connected in series between conductors 81and 8|. Biasing potentials are also provided in the tube 55b by means ofan extra pair of grids 98 and 91, the grid 98 being connected throughconductor 98 to one side of the B-battery 83 and to one end of theprimary of the.

output transformer 9|; and the grid 91 is connected through conductor 99to conductor 8| leading to one side of the' battery 58. A plate couplingresistor I80 is also preferably connected by conductor |8| between theplate of the tube 55a to the conductor 88 leading from the grid 98 oftube 55b.

In that part of the major circuit already described, we now haveimpulses from the sounds picked up by the microphone or other pick-updevice 11 amplified and applied across the primary 90 of the outputtransformer 9|. This output transformer is a step-down transformer andits secondary I02 feeds a pair of earphones I03 or other listeningdevice through conductors I04 and I05. As indicated in dotted lines,another listening device I03a, or as many more as may be desired, may beconnected in parallel with the listening device I03. Thus, one occupantof the vehicle carrying the present invention may have earphones I03aand microphone Ila, while another occupant may have earphones I03 andmicrophone I1, and these occupants may converse between themselvesutilizing the magnetic recording device only, there being no need for aseparate intercommunicating system in the -vehicle where in the magneticrecording device is utilized.

The primary 90 of the output transformer 9I is in circuit connectionwith the magnetiz ng coil I6 associated with the recording head. Theconductor 89 may be extended from the point where it connects with oneend of the primary coil 90 v to an end of an inductance coil I06, and ,aconductor I01 is connected to the other end of the coil I06 and to oneend of the magnetizing coil I6. To the other end of the magnetizing coilan extension of the aforesaid conductor BI is connected which returns toconductor 64 from the B-battery 63. A condenser I 08 is connectedbetween conductors 89 and BI and'is in parallel with the coil I06 andthe magnetizing coil 16 in series. This condenser I08 is of such valuethat the coils I06 and I6 are resonated in proper frequency, and it willbe noted that the use of the condenser I08 not only tunes themagnetizing coil 16 to give parallel resonance between the condenser I08and the magnetizing coil, but this arrangement in addition provides amarked economy in the use of various coils and inductances.

The primary 90 of the transformer 9I is tuned to a resonant condition bya condenser I09 connected between the conductors 89 and 9| on thetransformer side of the connections for the con denser I08. A blockingcondenser I,I is-incorporated in the conductor 89 near the primary ofthe transformer 9|, and this blocking condenser together with theaforesaid condenser 92 across the battery conductors 64 and 65constitute a low impedance input path to the magnetizing arrangement. Aresistor III of very high'resistance is also preferably included in theconductor 89 between the connections for the condensers I09 and I08 toprovide a low degree of coupling between the above described resonantcircuits.

The necessary high frequency voltage for the proper functioning of themagnetizing coil 16 is induced into the circuit by way of the inductancecoil I06 which isinductively coupled to an inductance coil II2 of anoscillating circuit or arrangement generally indicated by numeral II3which includes the oscillating tube 56 seen in Figure 3, and which neednot be specifically described herein, since the performance of such anoscillating circuit is understood by those skilled in the art. The highfrequency voltage induced in circuit with the coil I06, the magnetizingcoi1 I6, and the condenser I08 (this condenser pass ing high frequency)enables the magnetizing coil 16 to successively magnetize passingincrements of the recording medium 6 in keeping with variations in thesound picked up by the microphone It will also be especially noted thatwith the tuned circuit arrangement including the magnetizing coil I6 anyconversationbetween occupants of the vehicle carrying the recordingdevice, the

occupants utilizing the earphones I03 and I03a and the microphones TIand Ila, will be picked up and recorded on the recording. medium 6. Inother words, the magnetizing device will listen in on all conversationsbetween occupants of the vehicle and make a recording of thoseconversations. In the event the vehicle is an airplane,

all conversations between the pilot and some other occupant of thevehicle, or straight flight log by the pilot, will be recorded forfuture ref- 6. That medium may then be rescued from the wreckage, itbeing preferable to enclose the magnetic recording device in aflreproof'location, and the events leading up to the time of theaccident will be preserved,

It should further be noted that the circuit arrangement possesses adistinct advantage over previous circuit arrangements of which we areaware in that with th particular circuit connections from the primary ofthe transformer 9| to the recording head the maximum possible voiceenergy above background noise is recorded on the wire 6, andcompensation is made not only for wire characteristics but alsorecording head characteristics. It will be appreciated that the highfrequency portion of the circuit including the condenser I 08, thecoupling coil I06 and the recording coil 16 is isolated by virtue of thehigh resistance III. As stated above, the manner of providing a resonantcondition for the primary of the transformer 9| by the use of the tuningcondenser I09 and the manner of providing a resonant condition betweenthe coupling coil I06 and the magnetizing coil 16 by.

the use of the condenser I08, provides distinct advantages in simplicityof connections and economy of material and parts.

The necessary circuit connections from the battery of the vehicle to themotor I4 are illustrated in Figure 7. Line conductors Ill and H5 may beconnected to any suitable source of power, such as the vehicle battery,and extend to field winding II6 of the motor. One of these conductors,in the illustrated instance the conductor I I5, is provided with asuitable switch III. Conduc tors H8 and H9 extend from the conductors H4and H5 respectively to opposite sides of the armature of the motor I4,so that the armature is parallel with the field Winding. Parallel withthe armature by conductors I20 and I2I is a pair of condensers I2 andI3, also seen in Figures 3 and 5, and this circuit arrangement isgrounded between the condensers as indicated at I22. These condensers I2and I3 are preferably connected by very short leads on opposite sides ofthe motor armature and are for the purpose of eliminating noise,especially that created by any arcing that may occur at the motorbrushes. The aforesaid contact arms 20 and 22 of the motor governingarrangement seen in Figure 5 are connected to the conductor I9 by leadsI23 and I24. A resistance I25 is preferably embodied in the conductor H9in parallel with the contact arms 20 and 22. Likewise, the condenser 1|is also preferably parallel with both-the resistance and the contactarms. This condenser II is for the pur- 11 pose of quenching any arcsthat may occur during the making and breaking of the circuit between thecontact arms '20 and 22 andto prevent undue burning of the contactpoints carried by these arms. It will thus be seen that suitableprecaution for the elimination of noise and protection of parts of theapparatus have been taken in the relatively simple form of motor circuitincorporated in the instant invention.

In actual use, it is a simple expedient to place the magnetic recordingdevice in proper position in an airplane or other vehicle, and with thesingle connection to the plug 61 and terminals 68 of the'recordingdevice have the entire apparatus 'set up for the purpose of makingrecordings and insert a substitute container i, replace the plugs 69 and66, and the entire device is ready for instant use. The operation ofsubstituting anothercontainer 5| for the one already in use wouldrequirebut a very short interval of time. The defective circuit arrangement inthe removed container 5| may be then repaired at a convenient time in aground laboratory without requiring the loss of service of the devicewhen needed. Likewise, if the B-battery 63 should play out, it is asimple expedient to remove the plug 66, slide the B-battery out, andinsert a new B-battery already equipped with a plug 86 and insert theplug in the container 5|. As will be apparent to one skilled in the art,the facility of removing and replac- 'ing salient parts of the apparatusso that defective parts may be repaired at a convenient time and withoutloss of functioning of the apparatus, lends the invention to uses andpurposes too numerous to specifically mention herein.

From the foregoing, it is apparent that we have provided a magneticrecording device not only capable of functioning as such, but alsocapable of .the additional function of providing a means forintercommunication with the occupants of the vehicle without thenecessity of utilizing any apparatus other than that associated with therecording device. It will also be appreciated that the device may berepaired at leisure without loss of its function merely by the simplesubstitution of salient parts of the device. Further, it will be notedthat the device is self-governing, and the entire mechanism is simple inconstruction, occupies a minimum of space, and is so arranged a toprovide extremely high efflciency with comparatively few parts. Further,it will be appreciated that the device may be economically manufacturedand used.

It will, of course, be understood that various details of constructionmay be varied through a wide range without departing from the principlesof this invention and it is, therefore, not the purpose to limit thepatent granted hereon otherwise than; necessitatedby the scope of theappended c a s.

We claim as our invention:

1. In an electrical circuit for a magnetic recording device whereinsuccessive increments of a traveling recording medium are magnetized inaccordance with impulses being recorded, an oscillatory circuitincluding an oscillating coil, and a magnetizing circuit including acoupling coil in series with a magnetizing coil, said coupling coilbeing inductively coupled with said oscillating coil, and a condenser inparallel with said coupling and magnetizing coils to form therewith aresonant circuit.

2. In an electrical circuit for a magnetic recording device whereinsuccessive increments of a traveling recording medium are magnetized inaccordance with impulses being recorded, an oscillatory circuitincluding an oscillating coil, and a magnetizing circuit including acoupling coil in series with a magnetizing coil, said coupling coilbeing inductively coupled with said oscillating coil, a condenser inparallel with said coupling and magnetizing coils to form therewith aresonant circuit, and a resistance connected to one 3. In an electricalcircuit for a magnetic re cording device wherein successive incrementsof a traveling recording medium are magnetized in accordance withimpulses being recorded, an

oscillatory circuit including an oscillating coil,

and a magnetizing circuit includinga coupling coil in series with amagnetizing coilysaid coupling coil being inductively coupled with saidoscillating coil, a condenser in parallel with said coupling andmagnetizing coils to form therewith a resonant circuit, an amplifyingarrangement, a transformer of which the primary is fed by saidamplifying arrangement, said resistance being connected to the primaryof said transformer, and a condenser connected in parallel with. thefirst said condenser from a point between said primary and saidresistance to tune said primary to resonant condition, and a resistancebetween said resonant circuits to enable them to operate independently.

MARVIN CAMRAS.

RAYMOND E. ZENNER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,886,856 Warwick Nov. 8, 19322,235,126 Towne Mar. 18, 1941 2,306,162 Gipe Dec. 22, 1942 2,275,961Heller Mar. 10, 1942 2,335,277 Heller Nov. 30, 1943 2,321,812 HellerJune 15, 1940 2,038,647 Clausen ..Apr. 28,1936

661,619 -Poulsen Nov. 13, 1900 2,268,619 Reid Jan. 2, 1942 FOREIGNPATENTS Number Country Date 486,666 British June 8, 1938

